Wujûd (existence, finding) is essentially Allah's wujûd (which is the necessary wujûd without which nothing else would exist at all), whereas the wujûd (existence) of creation or of the contigent entities like human beings, angels etc. is a very limited and defined or a metaphorical*, 'borrowed' wujûd, so it is really necessary to distinguish between Wujûd Mutlaq (absolute existence) and wujûd mustafâd (borrowed existence).

Then it can be seen that from our human perspective we are held to affirm:

1.) on the one hand the absolute unlikeliness of Allah with anything created, called tanzîh or transcendance of God, (in Western metaphysics, where tanzîh is not as clear and consistent as in Islam, it gave rise to serious misconceptions) and

2.) on the other hand the likeness of Allah with creation, tashbîh. I.e. creation is manifestation, it is the "place of the Theophany"** where Allah makes Himself be known: as Allah says in a hadith qudsî: "I was a Treasure unknown then I desired to be known so I created a creation to which I made Myself known, then they knew Me."[3].
So man can conceive at least something of Allah's names or qualities.
For example Prophet Muhammad peace and blessings of Allah be upon him) told his Companions the story of the bird mother and her extent of mercy and compassion for her young ones. By drawing this example from the world, ie. from their human experience, they were reminded of the universal concept of mercy. At the same time this mercy "in the worldly realm" is only a trace of the vast Divine mercy and compassion (rahma), which sooner or later will overcome all negativity in created beings. As Allah says in another hadith qudsî:

"Truly My Compassion supercedes my wrath"

So concerning imân and `ilm one has to observe those two aspects of tanzîh and tashbîh and it is not possible to prefer the one aspect over the other when referring to Allah in His Divine function (al-Ulûhiyyah).

It seems that Shaykh Muhyi-Dîn Ibn `Arabi never used the notion of 'wahdat-ul wujûd' (oneness of being or existence) himself, it was used by those who came after him, f ex Al-Kashâni. The concept can be ambiguous, and therefore misleading. Instead Shaykh Muhyi-Dîn Ibn `Arabi used the notion of “`ain al-wujûd” (essence of existence). As it is these are all different terms of one reality, and it is our duty as muslims to realize the meaning of it, so as not to fall from the straight path of tawhîd .

So wahdat-ul wujûd is really `ain al wujûd, and it is formalized in the first part of the shahâdah, which states that in essence nothing really exists except the Real (Allah), because everything else has only a limited, defined, metaphorical*, borrowed wujûd.

And Allah knows best and most.

* metaphorical: expressing one thing in terms normally denoting another.
** manifestation: the recurrence of the creative act: tajrîd-ul khalq[3] A discussion of the 'Treasure-hadith' is here: [link]